The purpose of the proposed investigation is twofold. First, we wish to challenge the validity of the evidence in several recent scanning electron microscope (SEM) studies which have suggested that odontoblastic processes extend thouhgout the coronal dentine in human teeth. Although we do feel that the extent of the odontoblastic processes is greater than shown by previous transmission electron microscope (TEM) studies, we believe that the tubular structures observed in these SEM studies represent the inner hypomineralized sheath of the peritubular matrix and not the odontoblastic processes. To challenge these SEM interpretations, we will prepare specimens using the same methods as these authors and then embed the preparations for TEM examination; a method suitable for revealing the true nature of the tubular structures seen with SEM. Secondly, we wish to further explore the potential of a saw-microtome method for the fixation of the contents of the dentinal tubules. A saw microtome having a diamond edge blade will be used to cut horizontal and longitudinal sections of newly extracted and unfixed human 3rd molars. Rapidly penetrating fixatives (e.g. formaldehyde/glutaraldehyde) will be used to cool the cutting blade during sectioning and the 900um sections will then be immersed in the fixative for varying periods of time, embedded in Araldite and the entire section reduced to 75um on plastic microscope slides for light microscopic observations. Selected areas at varying distances from the surface of the pulp will be cut out of the large sections and processed for TEM. In addition, a SEM cast technique will be used to prepare fixed preparations of dentine which will subsequently be examined with TEM. The dentine matrix will be removed from some of the 75um sections with acid followed by hypochlorite and then re-embedded in Araldite. This effectively isolates the contents of the tubules; facilitating sectioning and the identification of structures which were in close approximation to the mineralized matrix. An appreciation of the nature of the contents of the dentinal tubules is paramount to understanding the mechanism and the morphological basis of pain transmission through the dentine. In addition, the role of the odontoblastic process and/or other tubular contents in responses such as dentine sclerosis needs further elucidation. Our studies should help clarify these issues.